Catheter locator apparatus and method of use

ABSTRACT

This disclosure relates to a method of catheter and radiating coil location in a human body and in particular to the determination over time of the location of the tip of a catheter as it is inserted and during its use in the body. In particular when a radiating coil is used in conjunction with a catheter, a coil locating device can be used to determine the distance the coil is from the device and hence its depth in the body of a patient. To assist a clinician using the coil-locating device, a display is provided that shows both a reference image of a part or portion of a body (non-subject body) and an image of the coil located on the display with reference to the reference image. This is achieved by locating the coil-locating device on or over a predetermined landmark on the patient&#39;s body.

CROSS REFERENCES TO RELATED APPLICATIONS

The present application is a continuation of U.S. patent applicationSer. No. 13/570,999, filed on Aug. 9, 2012, which is a continuation ofU.S. patent application Ser. No. 12/646,263, filed on Dec. 23, 2009, nowU.S. Pat. No. 8,265,732, issued on Sep. 11, 2012, which is acontinuation of U.S. patent application Ser. No. 10/362,273, filed onFeb. 21, 2003, now abandoned, which is a U.S. national phase ofPCT/AU01/01051, filed Aug. 23, 2001, which claims priority to AustraliaPQ 9592, filed Aug. 23, 2000 and Australia PR 5250, filed May 24, 2001,the entire content of each of which is hereby incorporated by referenceherein. The present application also relates to U.S. patent applicationSer. No. 13/857,819, filed on Apr. 5, 2013, the entire content of whichis hereby incorporated by reference herein.

This disclosure relates to a method of catheter and radiating coillocation in a human body and in particular to the determination overtime of the location of the tip of a catheter as it is inserted andduring its use in the body and/or its route through the body.

BACKGROUND

For ease of explanation, the guidance and placement and ongoingmaintenance of a catheter for enteral nutrition will be described in oneexample in this specification. It will however be clear to the personskilled in the art that the techniques and equipment described areuseful for similar placement requirements in other parts of the humanbody and animal bodies as well. Catheters are used for many differentpurposes and there exist many different catheter types. An example ofthe use of the disclosed apparatus in a human body will also be providedin the field of Central Venous Catheter location.

Enteral nutrition includes both the ingestion of food orally and thenon-volitional delivery of nutrients by tube into the gastrointestinaltract. Patients are candidates for enteral tube feeding that will not,should not, or cannot eat but who have a functional gastrointestinaltract. Benefits of enteral tube feeding are the maintenance ofgastrointestinal structure and functional integrity, enhancedutilization of nutrients, ease and safety of administration.

Enteral tube feeding is contraindicated for patients with diffuseperitonitis, intestinal obstruction that prohibits use of the bowel,intractable vomiting, paralytic ileus, and/or severe diarrhoea thatmakes metabolic management typical. Other potential contraindicationsthat depend on the clinical circumstances include severe pancreatitis,enterocutaneous fistulae, and gastrointestinal ischemia. Enteral tubefeeding is not recommended during the early stages of short-bowelsyndrome or in the presence of severe malabsorption.

The route selected for tube feeding depends upon the anticipatedduration of feeding, the condition of the gastrointestinal tract (e.g.esophageal obstruction, prior gastric or small-bowel resections), andthe potential for aspiration. The intestine can be accessed at thebedside (naso intestinal tube, naso endoscopic gastrostomy) or in theoperating room (gastrostomy and jejunostomy).

Nasal intubation for gastric feeding is the simplest and most often usedmethod for tube feeding. This technique is preferred for patients whoare expected to eventually resume oral feeding. Maximal patient comfortand acceptance is more likely when a soft feeding tube with a smallexternal diameter is used. Access to the duodenum and jejunum ispossible with longer tubes but placement of the tip into the duodenumand jejunum is more difficult and time consuming and has added riskfactors.

Enteral tube feeding is considered safer than parenteral nourishmentbecause mechanical, infection, and metabolic complications are usuallyless severe than those encountered with parenteral nutrition. However,enteral feeding is not problem free, and significant complications canoccur when the tube and feeding is managed by unskilled or untrainedindividuals or if monitoring is absent or inappropriate.

Incorrect placement of the feeding tube is one of a number of majorcomplications. Most serious is the unintended placement of the catheterduring nasal intubation into the cardiovascular system or into thelungs. Both of these situations are possible when inexperienced medicalstaff perform intubation. A stylet (relatively stiff small gauge wire)is used to stiffen and support the otherwise flaccid catheter tubeduring its intubation.

It is also prudent to check that the exit aperture of the feeding tube(typically located at the distal end/tip of the tube) remains in itsdesired location over the period of feeding. Protocols that address thisrequirement include frequent monitoring for the appropriate pH of fluidsextracted from the feeding tube while not carrying nutritional liquidsand careful patient monitoring to ensure that nutritional uptake is asexpected.

X-rays are often used to determine the location of the caudal/distal endof the tube. However, even X-rays are not necessarily conclusive as toits location. The natural and continuous movement of the internal organscan make it difficult for the physician interpreting the X-ray to besure of the actual location of the caudal/distal end of the tube becausethe movement described can change the position of the catheter overtime.

There exist a large variety of catheters, their names sometimesindicating their use, the part of the body they enter or treat andsometimes they are named after the physician or physicians who developedmethodologies for their use.

This disclosure also relates to catheter location methods and means forcentral venous catheters.

Intravenous catheters are those that access the interior of a patientvia an opening in the skin passed down one or more of the many branchesof the venous system to the region requiring medical attention. Thesetypes of catheters are also referred to as Venous Access Catheters (VAC)and Central Venous Catheters (CVCs) and are used generally in thecardiovascular system.

A sub-category of intravenous catheters is those that fall under theheading of Peripherally Inserted Central Catheter (PICC). Thesecatheters have been used by clinicians for many years and many differenttechniques exist for their insertion.

One such insertion technique is the Seldinger technique and along withadvances in devices and materials there now exists a modified Seldingertechnique, useful particularly for small or poor veins.

There exist a large selection of intravenous catheters such as forexample peripheral catheters which are used for insertion into the bodythat are from one half to three inches in length; midline catheterswhich are used for insertion being greater than three inches in length;mid-clavicular and non-tunneled sub-clavian, tunneled Groshong, Hickmanand Broviac or subcutaneous implanted ports for longer lengths.

Common to intravenous catheters is the use of a guide wire that ispassed into the body and into a vein and then directed by the skill ofthe clinician to the desired location. Once the guide wire is in place acatheter is slid over its external free end and pushed till the distalend of the catheter reaches the end of the guide wire.

The location of the tip of these types of catheters or the recordal ofthe advancement of the guide wire into the body is achieved in a numberof ways.

Return checks are used to expire types of liquids expected to be at ornear the tip of the catheter and the checking of length markings on thewires used within catheters are two methods used by clinicians who donot have ready access to alternatives. Ultrasound guidance, fluoroscopyand X-ray methodologies are preferred even though they do not alwaysprovide an exact determination of the location of the tip or path of theguide wire or catheter.

More expensive and more time-consuming CT examinations provide the bestmeans of locating not only the tip but also the path of any of the typesof catheter described above and others that are located in the body of apatient.

The final location of the caudal/distal end of any catheter is criticalto the efficacy of the purpose for the use of the catheter. In oneexample, the delivery of drugs directly into the heart can be bestachieved by the location of the caudal/distal end of the catheter in thesuperior vena cava (CVC). Studies show that it is preferable to locatethe caudal/distal end of the catheter in the upper portion of thesuperior vena cava (typically recognised as being more than 4.5 cm abovethe cavoatrial junction). Studies indicate that these preferablelocations appear to minimise catheter malfunction.

More critical however, is to ensure that the catheter is in the superiorvena cava itself, as there exist studies indicating that there is asignificant association between catheter malfunction and catheter tiplocation in the venous system adjacent to the superior vena cava.

FIG. 7 depicts the various veins in the vicinity of and including thesuperior vena cava.

Where for example, the catheter tip is in either of the brachiocephilacveins or near the junction of a brachiocephilac vein there is a greaterlikelihood of the unwanted development of a fibrin sheath or thepresence of thrombus around or at the tip of the catheter as compared tocatheter tips located in the superior vena cava. Greater likelihood ofunwanted developments can occur when a catheter tip is located in thesub-clavian vein or the cavoatrial junction or in the right atrium.

The effect of inappropriate or less than ideal catheter tip location isshortened survival which clearly is manageable but more serious effectsmay include thrombosis and phlebitis infections more, particularlypheumothorax infections and, in more serious situations, occlusions.

When catheter tips suffer thrombosis, these studies demonstratesignificantly shorter survival than those catheters that are not subjectto this unwanted development.

Appropriate patient care requires consideration of a large number offactors when considering the need for intravenous catheter usage.Sometimes the benefit of drug delivery has to be carefully weighedagainst the likelihood of adverse effects of intravascular devicerelated infections as mentioned previously.

Catheter selection is not a simple matter and factors to be consideredinclude the following:

-   -   type of medication    -   osmolarity and pH of the solution to be infused    -   duration of therapy required    -   secondary risk factors and chronic diseases    -   patient age, activities, work and lifestyle    -   future intravenous needs and long term prognosis    -   current availability and status of access veins (typically        peripheral veins of the limbs)    -   patient history of neurologic impairments, surgeries affecting        veins or lymphatic system, bloods dyscrasias, thrombosis and        previous intravenous use history    -   current patient diagnosis and preferences for treatment.

The anticipated duration of therapy can readily suggest short peripheralcatheters for periods of less than five days, and for periods of lessthan four weeks a midline catheter is generally suitable.

Midclavicular lines are an option and becoming more popular as theoccurrence of thrombosis resulting from sub-optimal placement insub-clavian regions other than the superior vena cava increase.

In fact mid-clavicular lines are often used in home care situations toavoid the time and cost of confirmatory X-rays. However, evenmid-clavicular lines need to be optimally placed in the lower one thirdof the superior vena cava, close to the junction of the superior venacava and the right atrium but should not advance into the right atriumitself.

The previously mentioned Peripherally Inserted Central Catheters (PICCs)having a tip location in the superior vena cava can be used for longterm therapy (five days to one year). However, they should be criticallychecked by X-ray to determine appropriate tip placement even though thisis neither a totally satisfactory nor certain method of locationchecking.

It is thus a real need for physicians to be able to increase theirconfidence that the catheter has been placed at the desired location andremain there in the body of their patient. This is so whether that isfor the purpose of enteral and parenteral nutrition, receiving vesicantchemotherapeutic agents, antibiotics and blood sampling or for otherpurposes.

BRIEF DESCRIPTION OF THE DISCLOSURE

An example embodiment of the present disclosure is a method of locatinga coil used in relation to a catheter to be inserted into a subject bodywherein said coil radiates signal energy; the method including the stepsof: using a coil position measuring means having at least two signalenergy detectors wherein said measuring means is located with referenceto a predetermined location on or part of said subject human body; anddisplaying a position measurement made by said coil position measuringmeans wherein said position measurement is relative to said positionmeasuring means for use by a clinician in determining the position ofsaid coil and said catheter in said subject human body relative to saidpredetermined location on or part of said subject human body.

In a further example embodiment, the method includes the further step ofalso displaying with said position measurement a representation of apoint or region of a non-subject body referenced to said displayedposition measurement for use by the clinician in determining theposition of said coil and said catheter in said subject human body.

In another example embodiment, the position measuring means is locatedwith reference to a predetermined location being on or over the xiphoidsternal junction of said human body for use with a catheter insertedinto the alimentary canal.

In another example embodiment, a region or delineation of a body part isdisplayed that is representative of the diaphragm of a non-subject humanbody thus delineating on said display the upper and lower chest cavitiesof a human body.

In another example embodiment, the position measuring means is locatedwith reference to a predetermined location being on or over thecaudal/mid sagital aspect of the jugular sternal notch of said humanbody use with a catheter inserted into the cardiovascular or respiratorysystem.

In yet another example embodiment, a region or delineation of a bodypart is displayed that is representative of the sternum of the saidhuman body thus delineating on said display a portion of the upperskeleton of a human body.

In a yet another example embodiment, the method includes the furtherstep of displaying a position measurement of said coil at predeterminedintervals of time.

In another example embodiment, the coil is incorporated into a stylet orguide wire adapted for use with a catheter.

In yet another example embodiment, the method includes the further stepof displaying the position of said coil at predetermined intervals oftime while said stylet or guide wire is retracted from a catheter sothat the path of said coil and thus said catheter can be tracked anddisplayed.

In another example embodiment, a coil is incorporated into a catheterand usable for locating the position of said catheter in a human body.

In another example embodiment, a catheter locator apparatus forassisting a user's placement of a catheter into a subject bodycomprises: a pair of wires usable with the catheter, the wires having afirst end and a second end; a processor in electronic communication withthe first end of the wires; a radiating coil connected to the second endof the wires, the radiating coil having various locations in the subjectbody; a detector device in electronic communication with the processor,the detector device adapted to be positioned in relation to apredetermined portion of the subject body; reference data retrieved bythe processor which specifies at least one reference image whichrepresents at least one predetermined image; indicator data generated bythe processor which specifies at least one indicator image whichprovides information related to at least one location of the radiatingcoil in the subject body; and a monitor in electronic communication withthe processor which displays the indicator image and the referenceimage.

In yet another example embodiment, a catheter adapted for use with acatheter locator apparatus includes: (a) a processor in electroniccommunication with a coil; (b) the coil radiating and incorporated intoa coil positioning device, stylet, guide wire or into said catheter, theradiating coil having various locations in a subject body; (c) adetector device in electronic communication with the processor; (d)reference data generated by the processor which specifies at least onereference image which represents at least one predetermined portion ofthe subject body; (e) indicator data generated by the processor whichspecifies at least one indicator image which provides informationrelated to at least one location of the radiating coil in the subjectbody; and (f) a monitor in electronic communication with the processorwhich displays the indicator image and the reference image, saidcatheter comprising: a tube which is adapted to receive the stylet orguide wire or having a coil incorporated thereto, the tube having aproximal end and a distal end; and a tip included at the distal end.

In another example embodiment, a catheter locator apparatus comprising:a multi stranded wire insertable into a catheter, the wire having aproximal end and a distal end; a radiating coil connected to the distalend of two of the strands in said wire; at least two receiving coils; amonitor; a processor, in electronic communication with the wire, thereceiving coils and the monitor, which: the processor receives at leastone reference signal from at least two of the receiving coils after thereceiving coil is positioned with reference to at least onepredetermined bony landmark on the subject body; and retrieves referencedata; and drives the monitor in order to graphically represent thereference data; and receives at least one indicator signal from the atleast two receiving coils that receive a signal from the radiating coilafter the radiating coil is inserted into the subject body; as well asgenerates indicator data; and drives the monitor in order to graphicallyrepresent the indicator data.

Another exemplary method of facilitating proper placement of a catheterinto a subject body, the method comprises the steps of:

(a) receiving at least one reference signal indicative of a location ofat least one receiving coil positioned with reference to a predeterminedlandmark on the subject body;(b) receiving at least one indicator signal from a radiating coilinserted into the subject body;(c) retrieving reference data associated with the predeterminedlandmark;(d) displaying a reference image derived from the reference data;(e) generating data represented by an indicator signal indicative of therelative position of the at least two receiving coil positions on orover the subject body;(f) displaying graphics represented by the indicator data; and(g) repeating steps (e) and (f) after a change in the indicator signalis received.

A further exemplary method of operating a catheter locator apparatus,comprises the steps of:

(a) placing a predetermined area of a detector device over apredetermined landmark on a subject body;(b) inserting a catheter, stylet, guide wire or coil locating device,embedded with a radiating coil, into the subject body;(c) viewing a graphical representation of a predetermined part orportion or a representation of a reference image on a monitor;(d) viewing a graphical representation of the radiating coil on amonitor; and(e) manipulating the catheter in the subject body with aid of thedisplay of the relative positions of the graphical representations.

Another example embodiment comprises a wire bundle for use with acatheter locator apparatus that includes: (a) a processor in electroniccommunication with a predetermined portion of a proximal end of the wirebundle; (b) a radiating coil connected to a predetermined portion of adistal end of the wire bundle, the radiating coil having variouslocations in a subject body; (c) a detector device in electroniccommunication with the processor, the detector device adapted to bepositioned in relation to a predetermined portion of the subject body;(d) reference data retrieved by the processor which specifies at leastone reference image which represents at least one predetermined image;(e) indicator data generated by the processor which specifies at leastone indicator image which provides information related to at least onelocation of the radiating coil in the subject body; and (f) a monitor inelectronic communication with the processor which displays the indicatorimage and the reference image, said wire bundle comprising:

a first wire having a predetermined stiffness adapted to controlpositioning of a flexible tube;

a second wire adapted to transmit signals between the radiating coil andthe processor; and means for binding the second wire to the first wire.

Specific example embodiments of the disclosure will now be described insome further detail with reference to and as illustrated in theaccompanying figures. These embodiments are illustrative, and are notmeant to be restrictive of the scope of the disclosure.

Suggestions and descriptions of other embodiments may be included withinthe description of the present application but may not be illustrated inthe accompanying figures or alternatively features of the disclosure maybe shown in the figures but not described in the specification.

BRIEF DESCRIPTION OF THE FIGURES

FIG. 1 depicts a catheter having a coil and exit aperture located nearits caudal/distal end.

FIG. 2 depicts a stylet having a coil located near its caudal/distalend.

FIG. 3 depicts a detector apparatus positioned appropriately on apatient and an outline of a display that delineates regions of the body.

FIG. 4 depicts a display of the location and depth of a coil on the tipof a catheter or stylet superimposed over a representation of a patient.

FIG. 5 depicts a typical display only of the coil position located inthe stomach of a patient over time even while it is not being moved intoa desired location;

FIG. 6 depicts the recorded path and the current location of a catheterin a patient as would be displayed.

FIG. 7 depicts the venous system of the upper torso.

FIG. 8 depicts an outline of a coil location device located in apreferred manner over the caudal/mid sagital aspect of the jugularsternal notch of a patient.

FIG. 9 depicts a pictorial representation of a correctly placed CentralVenous Catheter (CVC) in the superior vena cava of a patient.

FIG. 10 depicts a pictorial representation of the upper torso of apatient showing the path of a CVC and its tip in the region of thesuperior vena cava.

DETAILED DESCRIPTION OF EXAMPLE EMBODIMENTS

FIG. 1 depicts a single lumen catheter having located near itscaudal/distal end, a coil, which is used to emit a signal that can bedetected by an apparatus not unlike that described in U.S. Pat. No.5,099,845. That patent is in the name of Micronix Pty Ltd and is herebyincorporated into this specification by reference. The incorporation ofthe above-mentioned patent does not and should not be construed as anadmission of the content of the specification having entered the commongeneral knowledge of those skilled in the art.

The apparatus of the disclosure described in the above-mentioned patentprovides a means to determine both the depth and position of a coillocated on the end of a catheter as well as its orientation. The type ofcatheter is of no great importance to the principle and method of thedisclosure.

the depth and position determining apparatus, also referred to herein asthe detector apparatus, is generally of the type disclosed in theabove-mentioned specification and can be used in the method describedherein but is not the only such device that will provide the requiredfeatures.

The catheter 10 depicted in FIG. 1 is suitable for use in parenteralnutrition in particular as it has a suitable tip shape 12 designed sothat the exit aperture 14 is less likely to become blocked. The cathetershown has a single lumen (single passageway from proximal tocaudal/distal end) but other catheters may have multiple lumens.

A coil 16 is located near the tip 12 and the two ends of the pair ofwires, which will run the length of the catheter. The pair of wiresterminates at connector 18 near the proximal end of the catheter. Theentry aperture 20 to the catheter is located at the extreme proximal endof the catheter. It is into this aperture that nutrients are pumped atthe desired times and rates once the caudal/distal end of the catheterhas been appropriately located within the patient.

It is intended that the connectors for catheters used for different useswill each be different sizes, connection types and colors so as to maketheir use as safe as possible. By making the interconnection ofcatheters for different applications difficult if not impossible, it isintended to minimize accidental administration of the incorrect orinappropriate fluids particularly drugs to the patent via catheters notintended for such use.

When the catheter 10 is being intubated into the gastrointestinal tractof the patient, a metal stylet is used within the catheter.

The stylet can comprise the pair of wires described previously or cancomprise the typical stylet wire or wires having a pair of wiresincorporated therein. The stylet may be encapsulated in material know tobe suitable for its intended use. The stylet itself is typically made ofstainless steel but it could also be made of plastic or other suitablematerial as shown in FIG. 2.

In one embodiment, the processor is connected to a proximal end of awire bundle, and the coil is connected to the distal end of the wirebundle. The wire bundle includes a guide wire suitably bound to asignal-carrying wire/s. The bundle is preferably bound together at itsends and along its length and may also be encapsulated in material knowto be suitable for its intended use. The bundle may for example bewrapped together or wrapped with a suitable material, it may bemaintained by a suitable adhesive or fastener or suitable size andshape. See FIG. 2.

Intubation can be via the mouth or preferably via a nasal passageway ofthe patient. The stylet stiffens the otherwise formless catheter and isable to be manipulated along its length as well as at its proximal end,so that its caudal/distal end navigates an appropriate route through thepatient under the control of the health professional or trained staffperforming the intubation.

In this specification, mention is made of clinicians performingintubations but it is possible for trained health professionals toinsert catheters into patients for a variety of uses. It is alsopossible to use a suitably stiff catheter having a coil incorporatedinto the wall of the catheter typically at or near the caudal/distal endof the catheter that has a single lumen used to deliver the appropriatefluids.

The inventors have identified that there are economic and practicalreasons why the arrangement of a coil integrated into a catheter isusable. However, it is less desirable than an alternative arrangement tobe described herein which uses the stylet to carry the radiating coil.

The above is so, because the catheter/coil combination is expensive tomanufacture to the high standards required of medical equipment.Catheter manufacturers provide a specialist product and it is not alwaysin their interest to incorporate changes that will markedly increase thecost of their product.

Furthermore, a catheter/coil combination is a single use item, thus theadded value of the coil is not recoverable and therefore needs tocompete with current detection techniques which involve X-rays, eventhough they are more time consuming.

Thus it has been identified that it is possible to incorporate a coilinto the caudal/distal end of a stylet.

The stylet is used not only to manipulate the caudal/distal end of thecatheter to a desired location but it can be retracted and is alsocapable of being reused after appropriate decontamination and cleaningaccording to a required protocol. The inventors do not recommend suchreuse unless a relevant protocol is in place.

The depth and position of the coil can be determined during the processof intubation. Furthermore, when used to locate the tip of a catheterand following appropriate positioning of the caudal/distal end of thecatheter the route of the catheter can be determined while the stylet isretracted from the catheter. An example of the trace displayed after aretraction of the stylet is provided by FIG. 6 the details of which willbe described later in the specification. A stylet with a coilincorporated thereon can also be used to determine the location in thepatient of particular locations along the length of the catheter. Thusfor multiple lumen catheters that have a plurality of ports along itslength the location in the patient of each of those ports can bedetermined.

The manufacture of a coil on the end of a stylet is not trivial but itcan be automated and will involve only a few different materials, notthe many different material and processes involved in the manufacture ofa catheter/coil combination as described above.

As described previously a particularly advantageous feature of a coilbeing incorporated into a stylet is that while the stylet and coil isbeing retracted from the catheter, it is possible for the locationapparatus to record the route through the patient taken by the catheter.The route can be recorded, including its X-Y location and its depth withrespect to the detection apparatus. Most conveniently, the route of thecatheter can be displayed in a manner, which directly relates it to theanatomy of a patient. Appropriate positioning of the detection apparatuson the patient in the manner described later in this specificationprovides an ability to reference the position of the trace on themonitor with the position of internal parts of a patient.

Consequently, the procedure of re-checking the position of thecaudal/distal end of the catheter and retracing the route of thecatheter at future times can be easily conducted and the resultscompared with earlier records of the catheter tip position.

Furthermore, the route displayed will have characteristics that arelikely to reassure a clinician that a desired route of the catheter hasin fact been taken.

Over time, displays including depth information will correlate withother clinical observations as to the correctness of the placement andtherefore increase the confidence of the clinician that the route andfinal placements are as they should be.

The route displayed will, within expected anatomical variation, confirmthat the caudal/distal end of the catheter or other portions of thecatheter are located in the desired area of the patient. For example,when locating enteral feeding catheters, the region desired is thatwhich is in the vicinity of the jejunum, as is pictorially representedin FIG. 6.

It is also possible for these techniques to be used during theintubation process and thus provide immediate feedback as to the routebeing taken by the catheter.

The techniques described herein, which assist the placement of acatheter, are particularly applicable when tube enterostomies arenecessary to provide long-term nutritional feeding or when obstructionmakes nasal intubation impossible. A conventional gastrostomy orjejunostomy requires a surgical procedure and that is obviouslypreferably avoided.

Percutaneous endoscopic placement of gastric feeding tubes can beperformed at the bedside or in the endoscopy suite without generalanesthesia. Jejunal extensions may also be noted through a percutaneousplaced gastric port into patients who require post-pyloric intestinalfeeding. Needle catheter or Witzel jejunostomy placed at the time of thelaparotomy allows early postoperative feeding because the small bowel isless affected than is the stomach and colon by postoperative ileus.Jejunal feedings minimize the risk of vomiting and aspiration comparedwith gastric feedings.

However, the techniques described herein are not a substitute forcontrolled administration and careful monitoring to check for residualgastric fluids. Clinical observation of the patient must be continued.The technique however, does lessen or eliminate the costly and timeconsuming use of X-ray facilities and expertise or other even moreexpensive and time consuming catheter location procedures.

FIG. 2 depicts a stylet 22 which has a coil 24 at its caudal/distal endand the proximal ends of the wires which form the coil are located in aconnector base 26 and a manipulation block 28 is provided at the extremeproximal end of the stylet. The shape of the stylet is typically longand straight but shown in FIG. 2 conforms with the shape of the catheter10 shown in FIG. 1, for illustrative purposes only. The clinician iscapable of twisting the stylet, so that its caudal/distal end whenplaced inside and to the internal end of the catheter, turns thecaudal/distal end of the catheter to navigate various passages andapertures within the patient body. This twisting of the stylet is notrecommended but recognises a clinical practice noted in the literature.

FIG. 3 depicts an anterior view of the skeleton 28 of a patient andmarked in overlay are three circles representative of the preferredlocation of the three detector coils of the detector apparatus over thepatient's body.

The external shape of the detector apparatus is of little consequence tothe way in which the actual detector works but it is consideredadvantageous by the inventors that the external shape helps theclinician to appropriately locate the detector device on or over apredetermined location of the patient. For example a triangular shapeplaces the upper apex of the apparatus towards the head of the patientand the longitudinal axis of the apparatus can be made to lie coincidentwith the mid-sagittal line of the patient 32.

Circle 30 can be the most important of the three detector coil portionsas in this embodiment for the placement of the catheter in thealimentary canal (being that portion of the digestive system of thebody, including without limitation, the mucus membrane-lined tubeextending from the mouth to the anus including the pharynx, esophagus,stomach and the intestines) or in particular in the intestinal tract, itis positioned directly over the xiphoid sternal junction. This will alsoplace the longitudinal axis of the three detector coils coincident withthe median antero-posterior plane 32 of the body (mid-sagittal line).The longitudinal axis of the three detector coils is engraved on to thecase of the detector housing for the convenience of the clinician tofacilitate ease of positioning particularly since the xiphoid sternaljunction is typically easily palpitated.

The xiphoid sternal junction is the point at which the diaphragm isconnected to the human skeleton. The two arched lines (34 and 36) shownon the figure, are representative of the upper limits of the quitecomplex domes of the musculo-membranous partition (diaphragm) separatingthe abdominal and thoracic cavities and which serves as a major thoracicmuscle.

It is of assistance to the clinician that these two arched lines, 34 and36, are displayed on the monitor along with the mid-sagittal line 32 asis depicted in FIGS. 5 and 6, while the catheter is being located.

The display of the arched lines, 34 and 36 is a tangible consequence ofthe correct positioning of the detector coils in the manner described.The correlation of the position of the coil in circle 30 with thexiphoid sternal junction allows the monitor to depict the position anddepth of the coil with reference to a position of the body that can befound on all patients. It is not imperative that the coil be coincidentwith that particular bony landmark since the detector apparatus canaccommodate any predetermined offset created by having the outer housingof the apparatus located in a particular way that places the coil 30other than on or over the xiphoid sternal junction.

The device is relatively effective even if the specific coil 30 is notplaced precisely in the manner described. It is more important that thetwo or more signal detector elements are located on or over a part ofthe human body with reference to a predetermined part or position of thehuman body. Thus when the position of the coil on the end of the guidewire or catheter is displayed it can be displayed with reference to theapproximate position of a known body part or portion so as to assist theclinician during the placement process.

Clearly, the two arched lines 34 and 36 are only representations of thequite complex shape of the diaphragm. Since there is coincidence of atleast a portion of the representations with the attachment point of thediaphragm at the xiphoid sternal junction, the lines will besufficiently accurately depicted on the monitor to assist the clinician.With reference to the measurements taken by the sensor, therepresentation is an acceptable guide so as to provide confidence to theclinician that at least the caudal/distal end of the catheter is eitherbelow or above the diaphragm. Similar representations of parts orportions of the human body could be represented on a monitor referencedto the predetermined positioning of the detector coils.

As in most cases of intestinal intubation, once the caudal/distal end ofthe catheter/stylet is displayed as passing below the two arches thatrepresent the shape of the diaphragm, the clinician can be sure that thecatheter is in the gastrointestinal tract rather than in the airwaysand/or lung of the patient. Indeed, if the caudal/distal end of thecatheter were to be mistakenly routed into the lung, the path of thecatheter's caudal/distal end would be shown on the monitor to deviatefrom that expected.

The first noticeable deviation from the expected route would occur some10-cm above the two arches. That is, above the xiphoid sternal junction,at the level of the bifurcation of the trachea. This would also bemeasured as being deeper in the body from that which is expected of thecorrect route. Since the route shown in FIG. 4 is as expected for anintestinal intubation, it is on track to enter the stomach shown, ingeneral, as region 38. The catheter will then move medially and crossthe mid-sagittal line again at 40 entering the first part of theduodenum region 42 through the pylorus orifice. Once through theduodenum region 42, the catheter passes into the jejunum region 44 thatis the portion of the small intestine, which extends from the duodenumto the ileum.

It is also possible for the detection method and apparatus to be used tolocate particular portions of the catheter. For example, a dual cavitycatheter that is used for enteral feeding at its distal end anddecompression of gasses in the stomach along it length should ideallyhave the caudal/distal end located in the jejunum and the decompressioncavity extend no further that the pylorus orifice. If the decompressioncavity of the catheter begins a known distance from the distal end ofthe catheter then a stylet having a coil on its end can be drawn backfrom the distal end of the catheter that known distance. The position ofthe radiating coil can then be detected and compared with expectedposition measurements that will indicate whether the catheter iscorrectly positioned in the patient.

In another example, it will be advantageous to determine whetheraspiration or pressure measurement ports located along the length of acatheter are located at the desired position within the body of thepatient. This is the case not only at the time of intubation but alsoduring the time the catheter is being used.

The advantage of having a reference point or points on the monitor,which correlates with an actual point, region or structure of thepatient, is clearly apparent. This feature is useful during intestinalintubation but it is just as useful when locating a Venous AccessCatheter (VAC) which is a generic expression for the better knownCentral Venous Catheters (CVCs) some of which and their placement willbe described in detail later in this specification.

The monitoring of the passage of the catheter through the body andrechecking of correct location during treatment is enabled by means ofthe catheter locating apparatus described herein. Advantageously, thereis less erratic movement of the caudal/distal end of a VAC/CVC as it isplaced into location in the upper thoracic region because it is notdirectly in contact with internal organs of the body that move. Movementcaused by the breathing of the patient also affects the display of theposition of the catheter tip, much less in this application.

A monitor display that provides lines or a symbol (representative of letus say, the diaphragm) assists the clinician and increases theirconfidence that the correct path and final position of the caudal/distalend of the catheter has been achieved. However, the positioning of thedetector coils in relation to a predetermined reference point isimportant so that the lines or symbol displayed are correctly positionedrelative to the trace and properly reflect the position of the catheterin the body of the patient.

In the case of inserting CVCs with any of the catheter types or methodspreviously described, it is preferable to position the detectorapparatus over a well-defined, preferably bony landmark. In thisexample, a predetermined one of the three detector coils of the detectorapparatus is located over such a landmark. In the particular case oflocating the caudal/distal end of a Central Venous Catheter into thesuperior vena cava of a patient, it is preferable to locate coil 30, asdepicted in FIG. 8, on the caudal/mid sagittal aspect of the jugularsternal notch that lies along the mid sagittal line.

A possible detector apparatus shape 31 is also shown in FIG. 8. Theshape of the apparatus is of triangular form in plan view and ispreferable for its use on the chest of a patient as describedpreviously. This shape is convenient for the clinician to use becauseits apex 33 can be located on the caudal/mid sagital aspect of thejugular sternal notch and its longitudinal axis made coincident with themidsagittal line 32 of the patient.

As an aid to the preferable positioning of the detector apparatus, theexternal casing of the apparatus is preferably marked near its lowercorners “LEFT” and “RIGHT” respectively (not shown) ensuring a preferredorientation of this particular shape of apparatus in relation to thepatient. Additionally, it is useful to have a line marked or engraved onthe apparatus that runs along its longitudinal axis for assisting thevisual alignment of that line with the mid sagital line of the patient.However, it would be possible to have a differently shaped detectorhousing to suit other locations of use on the human body, whether thatis for general use or adapted for patient specific reasons.

The caudal/mid sagital aspect of the jugular sternal notch appears to bean ideal point on the body for positioning of the detector apparatus byclinicians as it is common to all humans and readily located visually orpalpitated regardless of the physical presentation of the patient.However, the use of the jugular sternal notch as a bony anatomy landmarkis not the only bony point or region of the body that could be used forthis purpose. There may be other points of the body to which themeasuring equipment can be reliably co-located or located with apredetermined offset. Such an arrangement allows the monitor to be usedto display a reference point or object, preferably shaped the same as apart of the body that will be useful to the clinician. Such as whenintubating a catheter or guide wire or checking the location of apreviously located catheter into which a stylet is located and retractedfrom.

The paths of the catheter/guide wire for enteral or CVC applications areshown in FIGS. 4, 6 as well as 9 and 10 respectively. These paths areideally represented paths. They are not what is necessarily seen by theclinician while using the locator apparatus during the process ofintubation of a catheter for enteral feeding or CVC positioning.

In practice the current position and depth of the signal emitting coilis displayed in a manner more like that shown in FIG. 5.

The coil at the caudal/distal end of the enteral feeding catheter whenused in certain body regions of a living patient will be subjected tocontinual movement due to the involuntary movement of the internalorgans of the patient. This can be due to the simple act of breathing(movement of the diaphragm). It can also be due to peristalsis (movementby the tubular organs such as the stomach, duodenum and jejunum in whichboth longitudinal and circular muscle fibres of those organs propeltheir contents). Furthermore there are other unavoidable movements thatoccur during the intubation procedure, although the extent of movementis much less for intubation into organs of the upper thoracic cavity.

Clearly, to provide the most useful form of display there needs to be abalance between the delay between drawing successive arrows (whichrepresent the current position, depth and orientation of the coil) andthe need to display the movement of the coil to the clinician. Too longan interval may allow the coil to traverse an unacceptable distancealong an incorrect path before it is recorded on the screen anddisplayed to the clinician. Too short an interval merely fills thescreen with arrows that appear to jump about due to the movement factorsdescribed above. Either of these cases may confuse or mislead theclinician rather than being of assistance.

The ideal delay is ultimately a matter of clinical preference and theapparatus can be adjusted by the clinician to deliver/provide a desireddisplay characteristics. Such a delay may be different when CVCcatheters are being inserted or being inserted into other regions of thebody.

The quantity of successively displayed location indicia is also a matterfor clinical preference and in the example shown in FIG. 5 there are 14successive positions shown at any one time. The tail of the displaydisappears as the route of the coil progresses through the internalorgans of a patient so as to keep to a minimum the number of indicia onthe screen at any one time. The monitor would otherwise become clutteredwith symbols, which would make it difficult to discern the relevantmovement and location of the current position of the caudal/distal endof the catheter/guide wire. Use of different colours to represent thenewest versus the last and intermediate indicators is also contemplatedto be advantageous to the clinician.

With regard to an enteral feeding catheter, once the caudal/distal endof the catheter is located in the area of the jejunum, a location mostsuitable for enteral tube feeding, the guide wire can be retracted. Atthis point the location and depth detection equipment can be used in arecording mode.

If the guide wire is retracted over a period of say three seconds, themonitor will be used to trace the path (X-Y and depth) of the coil as itpasses back through the route of the then properly located catheter. Thedetector apparatus is arranged to record the radial distance of theradiating coil from the two or more detector coils at predeterminedintervals suitable for providing enough measurements to calculate a lineof best fit. Clearly the more measurements the better the line of bestfit will be. There are however, many techniques for transforming suchmeasurements into a visual indicator of the route of the coil as it isretracted from the catheter. Those skilled in the electronic andcomputing arts would readily be able to provide such functionality.

The change in the signal detected can be used to determine the pathbeing taken by the radiating coil and there exist many other ways inwhich the activity of the coil can be detected and processed to bedisplayed. A further way would be to display the coil position each timethere is a predetermined change. The actual change required would becontrollable by the user to suit the type of use the radiating coil wasbeing put to at the time.

A processor having computer functions would be one of many ways ofperforming the comparisons of various signals received by the detectordevice, that as is disclosed in the referred to US patent by theapplicants, comprises three coils set in a particular spatialrelationship.

The processor would produce indicator data based on the signals receivedand processed by the processor. The processor can then also produceindicator data representative of the position of the radiating coil inthe form most useful to the user of the apparatus. One such form is anindicator image. The figures display an arrow symbol that is anindication to the user of the position and direction of the coil beingdetected. This particular indicator image is useful but there will bemany as useful alternatives.

The processor will also be capable of producing reference data thatspecifies a predetermined reference image. The reference image could bethat of any line, curve or object. Preferably, the reference image isthat of an appropriate part or portion of a body. That part or portionis not the actual part or portion of the patient being intubated butrather a created pictorial representation of such. In particular itcould be of a non-subject body (that is not the patient). As statedpreviously, it is intended that different types of catheter locatingapparatus be made to be incompatible it may be possible to use a commondetector device. However, in the case of there being different devicesit may not be necessary for them to provide any indication to theprocessor of their type. Since the two would be made for each other itmay be possible for a data storage device containing one or morepredetermined reference images to be available. Thus the data storagedevice can be used to provide an appropriate image of say a sternum forthe type of detector device and its location being used. The datastorage device can also provide storage for symbols and other imagesuseful in displaying information on a display relating to the positionof a radiating coil (indicator data) used with a catheter and areference image (an appropriately located symbol of a point or part of abody).

The display shown in FIG. 6 is a typical result, which shows a trace ina particular patient. Other patients may display a slightly differentpath and depth. The depth measurements shown is a relative measure andnot an absolute, but used in the appropriate way it can greatly assisttrained and experienced personnel intubating a catheter into a patient.

Thus the relative depths of the tip of the catheter are taken greatestnote of since the ratio of change from person to person will very likelybe small.

In an example of an enteral feeding catheter intubation the displayshown in FIG. 6 shows that when the catheter passes below the xiphoidsternal junction 30 it is very deep (say 17 cms below the location ofthe detector device). While the catheter passes through the stomach, itstip lies closer and less deep (say 14 cms) and when passing under themid sagital line 32 it is very shallow and closest to the surface of thepatient (say 8 cms). In the first part of the duodenum it is relativelyshallow (say 10 cms) and finally becomes very deep (say 17 cms) when inthe duodenum/jejunum.

After long term clinical use, an acceptable and reliable range of depthsand ratios at the points or regions described above (or others) will bedeveloped and most useful for assisting clinical assessment of thecorrectness of the route taken by the catheter.

Again, it can be seen that although not proof of the exact location ofthe caudal/distal end of the stylet mounted coil and hence the tip ofthe catheter, the displayed characteristics provide yet another aid toimproving clinical decision making in respect of the location of acatheter.

A stylet is capable of being reused in a catheter (after decontaminationand cleaning). Thus, it can be cheaper to use in a clinical environmentand encourages more frequent checking of the catheter location thanwould otherwise be the case because the expense and time consumingnature of X-ray or other detection methods. Stylet reuse, althoughcommon in the clinical environment, is not recommended by the authors ofthis document, until there is regulatory approval under a code ofpractice governing re-use of such devices.

It should not of course be forgotten that other clinical monitoringtechniques should continue to be used thereby increasing the confidenceof the clinician that the catheter is appropriately located, whetherthat be for enteral/parenteral nutrition or other purposes.

Patients are often intubated with VAC/CVCs using image guidance by meansof X-rays, fluoroscopy and ultrasonography. Percutaneous central venousaccess is achieved when the tip of a catheter is located in the cavalatrial region. Tunneled catheters travel through a subcutaneous tractprior to exiting the body via an incision in the skin. Such cathetersare used for medicament delivery and dialysis. Image-guided techniques,although expensive, are less fraught with early complications than blindor external landmark intubation techniques.

VAC/CVCs are now used for long-term intravenous antibiotic support aswell as parenteral nutritional support and blood sampling.

A selection from the many types of VAC/CVC in the marketplace caninclude single- or multi-lumen short-term “central lines”, tunneledcatheters, such as Hickman™ or Groshong™, and implanted catheters, suchas Port-A-Cath™ or InfusaPort™. In addition, Peripherally InsertedCentral Catheters (PICCs) are also available.

The example embodiments described herein can assist in the correctplacement of most catheters and most advantageously can be used to checkand confirm their correct placement at any time following initialplacement.

FIG. 7 depicts an anterior view of the venous system of the upper torsoshowing the right subclavian vein 46 and the left subclavian vein 48which meet medially with corresponding right and left brachiocephalicveins 50 and 52 respectively.

The junction of the brachiocephalic veins occurs at the upper region ofthe superior vena cava 54, which descends towards the cavoatrialjunction 56 prior to entering the right atrium 60 of the heart 62.

FIG. 9 depicts, as would be seen on a screen visible to the clinician, aconstructed trace 64 of the path of a Peripherally Inserted CentralCatheter (PICC) which has its tip ideally located in the central regionof the superior vena cava 54. FIG. 9 also depicts an outline of asternum 66 thus providing a region of reference for the clinicianbetween what is shown on screen and a known landmark of the patient'sbody. Clearly, the outline is a pictorial representation of a genericsternum and not the sternum of the patient. This representation is, inany event, useful to the clinician for the task at hand.

During placement of the PICC, because of the relative stability of theorgans above the diaphragm of the patient, the feed in trace provided ona monitor will be similar to the pull back trace described in respect ofenteral feeding catheters. It will be clear that the tip of the catheterhas entered the superior vena cava from not only the two dimensionalroute displayed on the monitor, but also confirmed by its depth as itwends its way through the various branches of the venous system in theupper torso of the patient while being feed over the previously insertedguide wire.

Most obvious to the clinician from the monitor will be the sharp changein direction and relevant depth of the catheter as it transitions fromthe subclavian vein into the brachiocephalic vein (68 of FIG. 9).

As described previously, an independently identified measure of the mostpreferred location of the tip of the catheter occurs when, in an adult,there is about 9 cm of linear distance between the catheter tip and theappropriately located measuring instrument. This is with reference towhen a detector apparatus has been placed on the caudal/mid sagitalaspect of the jugular sternal notch along the midsagittal line of thepatient.

Such an explicit measurement is used herein as an example only, of thepractical methodology associated with the use of the device but it maywell not be totally accurate for all circumstances. Such measurementsthough, are likely as described previously, to become clinicallyacceptable as an indicator of the appropriate location of the tip of thecatheter as the number of patients measured increases and verificationby other methods occur and further data is gathered and analyzed in thefuture.

The display is particularly useful to the clinician as the progress ofthe tip of the catheter is continuous and always displayed withreference to, in this embodiment, the position of the patient's sternumas is indicated by the shape 66 on the monitor display.

FIG. 10 depicts some of the venous system of the upper thoracic cavityand in particular the placement of a PICC 70 terminating in the superiorvena cava.

It should be apparent from the foregoing that the part or portion of thebody displayed is not used to explicitly locate the signal radiatingcoil with reference to it but is used more as a guide.

The clinician will learn from their observations over time that theposition of the inserted coil as determined by the signal detectorsindicates a radial distance of X cms relative to a predeterminedlocation on the signal detector apparatus and not the displayed symbol.The processor will be capable of providing the coordinates, in say X andY in the horizontal plane (assuming a supine patient) of the location ofthe coil both as an image on the screen but also in figures.

When the signal detector apparatus itself is consistently located withreference to a predetermined body part or portion thereof, eachmeasurement displayed will be referenced to the displayed referenceimage. However, this is not meant to be an absolute and what theclinician experiences and assesses as the actual position in say aparticular organ or channel in the body is a matter of acquiredexpertise.

Thus the display is used on two levels. One is to provide accurateradial distance X or (X,Y) from a predetermined point on the detectorapparatus. The other is to reference that position measurement to aknown body part or portion thereof (that might be a different one tothat displayed).

The body part or portion displayed is only pictorial. It is only used asan indicator of a region.

The arched lines (depicted in FIGS. 3, 4 and 5) represent as discussedpreviously the complex shape on a vertical cross-section of thediaphragm of a typical human. Since the electronics used in the detectorapparatus and the display expect that the upper coil of the detectorcoils has been placed on a particular bony landmark, the display canshow the position the junction of the two curved lines and reference themeasurements of the position of the catheter coil accordingly.

It is thus possible, even recognizing that the display is only anindicator, to provide prompts additional to the obvious visual ones.These prompts may inform the clinician that the signal-radiating coil isabove or below the arched line indicative of the diaphragm of thepatient. These prompts could be in the form of audible signals.

Say for example, audible tones may increase in frequency as the depictedcoil position gets closer from above the arched lines assuming that thehead end of the patient is correctly determined by correct placement ofthe detector device. Furthermore, as the coil position displayed movesbelow and a way from the displayed arched lines an audible tone maypluses less quickly the further it moves away.

The audible signals could be of a type that is preferable to the user ofthe apparatus.

It is also possible for the measured position to be used to indicate thepossibility of an incorrect placement. This requires the equivalent ofan expert system information database to be programmed into the displaydevice. Ideally, for a predetermined location of the signal detectorapparatus on the body, there are defined regions in the body consistingof certain radial distances from the signal detector, that if measuredduring an intubation would indicate that the signal radiating coil is inor approaching an undesirable region or part of the body.

Thus not only does the clinician form over time a feel for the expectedposition measurements but the expert system can be used as a backup towarn the clinician of the progression of the radiating coil and thus thecatheter into an inappropriate region of the patient. This furtherindication can be by way of visual indicators on the monitor screen orby additional audible signals. Recognizing that there are variations inthe anatomy of the human body from patient to patient, it is importantto note that the method described provides guidance and is no substitutefor clinical experience.

As clinical experience accumulates with the placement of catheters inother parts of the body, it will be possible to overlay on a monitorother reference images such as representations of static points,regions, or structures of the anatomy that may assist the clinician.Additional visual and audible information can also provide guidance tothe skilled clinician or registered nurse authorized to locate cathetersinto patients.

It will be appreciated by those skilled in the art, that the disclosureis not restricted in its use to the particular application described.Neither is the present disclosure restricted in its preferred embodimentwith regard to the particular elements and/or features described ordepicted herein. It will be appreciated that various modifications canbe made without departing from the principles of the disclosure.Therefore, the disclosure should be understood to include all suchmodifications within its scope.

The application is claimed as follows:
 1. A catheter locator systemcomprising: a processor; a display device operatively connected to theprocessor; a detector device operatively connected to the processor, thedetector device being configured to be positioned over a predeterminedlocation of a subject; a coil operatively connected to the processor,the coil being configured to be inserted into a catheter; and a memorydevice storing: (a) a first predetermined delineation representative ofa mid-sagittal line of a subject; (b) a second predetermined delineationrepresentative of a diaphragm of the subject; and (c) instructions whichwhen executed by the processor, cause the processor to, in cooperationwith the display device, the detector device, the coil and the memorydevice, while at least one of the coil is being advanced and the coil isbeing removed from the catheter: (a) display the first predetermineddelineation representative of the mid-sagittal line of the subject andthe predetermined delineation representative of the diaphragm of thesubject; (b) for an esophageal segment, determine and display a firstposition including a first depth of the coil in relation to the detectordevice; (c) for a stomach segment, determine and display a secondposition including a second depth of the coil in relation to thedetector device; (d) for a pylorus segment, determine and display athird position including a third depth of the coil in relation to thedetector device; and (e) for a duodenum segment, determine and display afourth position including a fourth depth of the coil in relation to thedetector device.
 2. The catheter locator system of claim 1, wherein aroute of the coil through the subject body is recorded.
 3. The catheterlocator system of claim 2, wherein the route includes at least an X-Ylocation.
 4. The catheter locator system of claim 1, wherein the firstpredetermined delineation and the second predetermined delineationintersect at a point representative of a xiphoid sternal junction of thesubject.
 5. The catheter locator system of claim 1, wherein the coil isconfigured to transmit electromagnetic signals.
 6. The catheter locatorsystem of claim 1, which includes a plurality of wires having an endportion which is connected to the coil, the plurality of wires being atleast one of a stylet and a guide wire.
 7. The catheter locator systemof claim 1, wherein the detector device includes a plurality ofreceiving coils which receive electromagnetic signals from the coil. 8.The catheter locator system of claim 1, wherein arrow symbols which areindicative of a direction of travel of the coil are generated anddisplayed.
 9. The catheter locator system of claim 1, wherein theinstructions, when executed by the processor, cause the processor to, incooperation with the display device, the detector device, the coil andthe memory device, while at least one of the coil is being advanced andthe coil is being removed from the catheter, for a jejunum segment,determine and display a fifth position including a fifth depth of thecoil in relation to the detector device.
 10. A catheter locator systemcomprising: a processor; a display device operatively connected to theprocessor; a detector device operatively connected to the processor, thedetector device being configured to be positioned over a predeterminedlocation of a subject; a coil operatively connected to the processor,the coil being configured to be inserted into a catheter; a memorydevice storing: (a) a first predetermined delineation representative ofa mid-sagittal line of a subject; (b) a second predetermined delineationrepresentative of a diaphragm of the subject; and (c) instructions whichwhen executed by the processor, cause the processor to, in cooperationwith the display device, the detector device, the coil and the memorydevice, while at least one of the coil is being advanced and the coil isbeing removed from the catheter: (a) display the first predetermineddelineation representative of the mid-sagittal line of the subject andthe predetermined delineation representative of the diaphragm of thesubject; (b) for an esophageal segment, determine and display a firstposition including a first depth of the coil in relation to the detectordevice; and (c) for a stomach segment, determine and display a secondposition including a second depth of the coil in relation to thedetector device.